This invention relates to an access system in which the optical pickup of an optical-disc reproducing apparatus accesses a track on the disc, and particularly to an access system which enables the pickup to move at high speed, for high-speed accessing of a track without vibration of a lens.
There is known an actuator having an object to lens for an optical disc-reproducing apparatus, wherein the object lens is moved in the focus direction (optical-axis direction) in order for the light beam to be focused on the disc and the object lens is moved in the tracking direction (perpendicular to the optical axis) in order to follow a track on the disc. Servo technology which employs a feed-back circuit. Such as the tracking servo circuit disclosed in U.S. Pat. No. 4,525,823 titled "OPTICAL TRACKING SYSTEM " may be utilized for the device of the pickup in each direction. When the light spot is moved to one of the discontinuous positions on a rotating disc, a pickup is moved in the radius direction to make access to a different track under the condition in which the tracking servo system is cut off, and therefore, the object lens which is free, or movable on the pickup is vibrated in the track direction when the pickup is accelerated or decelerated. When the pickup arrived at the target track position to be accessed, the object lens is vibrated, resulting in poor pulling operation for tracking; that is, it follows that the light beam passing through the object lens when the tracking servo is again on, does not follow a certain track, takes a long time to follow or takes a different time to follow each time.
In addition, since pulling operation is uncertainly made somewhere in the tracking operation range of the lens, or since the pull operation is not always made at the position where the optical axis of the pickup is coincident with the center of the object lens held on the actuator of the pickup through the suspension, the amount of movement of the pickup sometimes actually varies over a large range of movement.
In order to cope with the above problem, a position sensor is attached to a movable portion of the actuator of the optical pickup so that the lens is controlled to be locked by the servo technics during access (when the pickup is travelling), as is disclosed in a digest of technical papers presented at the Topical Meeting on Optical Data Storage Optical Society of America, Apr. 18-20 1984, Montery, Calif., titled "A Fast Random Access Servo System Utilizing A Digital-Audio Optical Pickup" by Scott Hamilton, Tony Lavendender and Larry Dillard, FC-B4-1, and "A Two Axis Linear Servo Motor For Optical Recording" by Thomas E. Berg, FC-B2-1.
According to these citations, the actuator becomes very complicated in construction, and since the weight of the movable portion increases, there is a possibility that the basic performance of the actuator including the movable portion and a magnetic circuit for moving the movable portion is deteriorated.